Field of the Invention
The present invention relates to a glass-fiber-reinforced thermoplastic resin molding product having a strength improved by dispersing glass fibers therein, and a production method therefor. More specifically, the invention relates to a glass-fiber-reinforced thermoplastic resin molding product which has a ring-shaped structure and exhibits excellent performance for use as a mount, a bush or a torque rod.
Description of the Related Art
Parts for use in automotive engine rooms are required to have sufficient physical properties, e.g., sufficient strength, water resistance, heat resistance and resistance to calcium chloride (which is used as a snow melting agent), under higher temperature and higher humidity conditions. Conventionally, these parts are generally made of metal. In recent years, it has been contemplated to use automotive parts made of a fiber-reinforced resin (FRP) instead of the metal automotive parts to meet a need for weight reduction. Particularly, a glass fiber reinforcement thermoplastic resin containing glass fibers dispersed therein is excellent in versatility, processability, moldability and the like and advantageous in terms of costs and, therefore, is expected to find applications in the aforementioned field. A glass-fiber-reinforced thermoplastic resin molding product is typically produced by melt-kneading the thermoplastic resin together with glass fibers, pelletizing the resulting mixture, melting the resulting pellets again and injection-molding the resulting melt (see, for example, JP-A-2012-25844, JP-A-2003-285323 and JP-A-2010-189637).
Where the intended molding product is produced by once pelletizing the glass fiber/thermoplastic resin mixture, however, the glass fibers are broken by a shear stress in a melt-kneading machine during the pelletization to be thereby reduced in size (to a fiber length of not greater than 0.5 mm), and further receives a shear stress during the injection molding to be thereby further reduced in size. Therefore, the glass fibers present in the molding product thus produced are excessively reduced in size, so that the molding product strength improving effect is problematically reduced.
To cope with this, it is contemplated to use filament reinforcement resin pellets (pellets containing glass filaments prepared as each having a longer fiber length by a drawing method). However, this adversely influences the moldability and, where a molding product such as a mount, a bush or a torque rod having a ring-shaped structure is produced, the molding product has a greater residual stress in the presence of the filaments. Further, a resin having a lower molecular weight should be used to increase the penetrability of the resin to the glass filaments. Problematically, this makes it impossible to impart the molding product with sufficient strength. JP-A-2003-285323 and JP-A-2010-189637 propose methods in which filament reinforcement resin pellets and staple fiber reinforcement resin pellets are mixed together and the resulting mixture is used for the molding. This improves the moldability, but the problem associated with the residual stress is not solved because the fiber length distribution has a double peak profile.
Where the molding product molded from the conventional glass fiber reinforcement thermoplastic resin as having the ring-shaped structure has a smaller wall thickness, the molding product problematically has a reduced mechanical strength, particularly, in a high temperature atmosphere or in a moisture absorbed state. This problem is solved by increasing the wall thickness of the molding product, but the weight reducing effect is problematically reduced.
WO2012/124060 proposes a method for producing an intended molding product by preparing fiber reinforcement resin materials for a skin layer and a core layer respectively having different flexural elastic moduli and sandwich-molding the materials to solve the aforementioned problem. However, the sandwich-molded product has a layer interface and, therefore, is liable to have an insufficient strength. Further, the sandwich-molding requires a special molding machine, thereby increasing production costs.
In view of the foregoing, a glass-fiber-reinforced thermoplastic resin molding product is provided, which has excellent mechanical strength in a high temperature atmosphere or in a moisture absorbed state even without imparting the molding product with a greater wall thickness or taking other measures, and has sufficient distortion resistance and sufficient strength as required for a ring-shaped structure, and a production method therefor is provided.